1. Field of the Invention
The present invention relates to anthracycline derivatives, and more particularly, to processes for the selective demethylation of anthracycline derivatives.
2. The Prior Art
The anthracyclinones of the formula: ##SPC3##
Wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are independently selected from the group consisting of hydrogen, chlorine, bromine and methoxy, with the proviso that at least one of the substituents is methoxy, and wherein R.sub.5 is selected from the group consisting of hydrogen, OH, OR and OCOR, in which R is an alkyl group containing 1 to 4 carbon atoms, are intermediates for the production of known useful antibiotics and anti-tumor agents, such as daunomycin, adriamycin and analogues thereof. For example, compounds of formula (I) can be converted to daunomycin, adriamycin, etc., by the methods described in co-pending applications Ser. Nos. 560,104 and 560,105 as well as in U.S. Pat. No. 3,803,124, all owned by the unrecorded assignee hereof.
Heretofore, compounds of formula (I) have been obtained in only very low yield, through a 4-step procedure, starting from a compound of the formula: ##SPC4##
Wherein R.sub.1, R.sub.2, R.sub.3, R.sub.4 and R.sub.5 are as defined above. For example the compound of formula (I), wherein R.sub.1 = R.sub.2 = R.sub.3 = H and R.sub.4 = R.sub.5 = OCH.sub.3, has been obtained (C. M. Wong et al, Canad. J. Chem., 51, 466, 1973) from a compound of formula (II), wherein R.sub.1 = R.sub.2 = R.sub.3 = H and R.sub.4 = R.sub.5 = OCH.sub.3, in only 10% yield according to the following reaction sequence: ##SPC5##